This invention relates to laser shock peening of a part and to a tape, which includes an ablative medium for producing localized compressive residual stresses in the part.
Laser shock peening (LSP) is a process for producing a region of deep compressive residual stresses over a surface area of a work piece such as a part of a turbine engine. Laser shock peening typically uses multiple radiation pulses from high power lasers. The pulses or xe2x80x9chitsxe2x80x9d produce shock waves on the part surface. The part surface is generally coated with a paint or tape, which functions as an ablation material. Some amount of the ablation material vaporizes from contact with the laser beam. The rapid vaporization produces a shock wave which travels into the metal, creating compressive residual stress through plastic deformation. A confining medium can be employed to direct the shock waves into the part. The confining medium comprises a transparent layer of material such as a transparent plastic or a curtain of water. The LSP process creates compressive stresses in the part, which considerably increase resistance to fatigue failure.
Ablative tapes have been developed to provide the LSP ablation material. The tapes can comprise an adhesive layer on one side of an ablative layer. However, an ablative tape typically used in an LSP process can degrade during use. The degradation may be due to repeated pulses of the laser beam to the same tape area. Degradation of the tape results in xe2x80x9cburn spotsxe2x80x9d and damage to the underlying part surface. The part can be repeatedly re-taped to prevent same area pulse damage. However, re-taping is time consuming, labor-intensive and costly.
There is need for an LSP tape process that requires decreased retaping. In addition, there is a need for an improved, resilient ablative tape for use in an LSP process.
The invention provides an improved ablative tape that withstands repeated application of laser pulses. The tape comprises an ablative medium comprising a polymer and dispersed metallic component.
In an embodiment, the invention relates to a method for treating a surface of a substrate. In the method, a tape is applied onto a substrate surface. The ablative tape comprises an ablative medium comprising a polymer and dispersed metallic component. The tape is then irradiated to ablate the ablative medium.
In another embodiment, the invention relates to an article, comprising a substrate and an ablative tape applied to the substrate. The ablative tape comprises a polymer and a dispersed metallic component.